Lithium soap-synthetic base instrument grease



LITHIUM SOAP-SYNTHETIC BASE INSTRUMENT GREASE Charles H. Culnane and John P. Dilworth, Fishkill, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application December 7, 1951, Serial No. 260,588

6 Claims. (Cl. 25242.1)

This invention relates to an improved lubricating grease composition suitable for use over a wide temperature range, and more particularly to a texture-stable lithium base grease of superior low temperature properties in which the oil component is a mixture of an aliphatic diester and a mineral oil.

Greases suitable for the lubrication of high speed ball and roller bearings over a temperature range from about 300 F. to about 67 F. have been developed employing aliphatic diesters of high molecular weight as the oil component with lithium soaps. The aliphatic diesters employed for this purpose have been ordinarily those within the viscosity range from about 10 to 15 centistokes at 100 R, such as di-2-ethylhexyl sebacate. They have been employed either as the sole lubricating oil component of the grease or in admixture with very light lowpour point mineral lubricating oils, usually within the viscosity range of about 5 to centistokes at 100 R, such as were employed as the oil component of low temperature greases before the development of these synthetic oils. A very superior grease of this type having exceptional shear-resistance properties is described in U. S. 2,450,222, Ashburn, Barnett and Puryear, wherein the lithium soap is obtained from a hydroxy fatty acid inaterial, which is most suitably a mixture of hydrogenated castor oil and stearic acid in about a 3:1 proportion by weight.

However, greases of the above type which have been proposed heretofore are not suitable for use at temperatures down to 100 F., as required for the lubrication of the newer types of military aircraft, and it has not been possible to formulate satisfactorily a grease meeting the requirements of the new proposed government specification for a low-temperature grease for this type of service from the teachings of the prior art. Greases wherein the oil component is an aliphatic diester within the viscosity range from about 10 to centistokes, as have been ordinarily employed heretofore, have too high low temperature torques and apparent viscosities at 100 F. to meet the requirements of this specification. When less viscous esters, having viscosities at 100 F. below about 10 centistokes, are employed as the sole oil component of these greases, either an excessively large 2,721,844 Patented Oct. 25, 1955 ice ture modifier of the high polymer type must be employed in order to obtain a grease of satisfactory body and stability. The use of 'such high polymeric materials is undesirable in greases of this type because of the tendency of polymer additive oils to break down under high shearing stress. Blends of aliphatic diesters and mineral lubrieating oils such as have been proposed heretofore are un- I suitable for producing greases to meet the new specificaamount of the very expensive lithium soap or a str uc- I tions because of unsatisfactory high and/ or low temperature characteristics which they impart to the greases.

We'have now found'that very satisfactory greases for the lubrication of aircraft accessories down to F. and meeting .all the requirements of the new proposed specification for such low temperature greases are obtained by employing a lithium soap of a soap-forming hydroxy fatty acid with an oil component which is a mixture of a relativelylow viscosity aliphatic diester, having a viscosity at 100 F. below about 10 centistokes, and a small proportion of a much higher viscosity mineral lubricating oil. We have found surprisingly that, by the use of small proportions of relatively high viscosity mineral lubricating oils in combination with such diesters, the amount of lithium soap required to produce a grease of a given grade is very greatly reduced, and the greases obtained have lubricating properties which are unexpectedly superior to those wherein the diester comprises the sole oil component.

In accordance with our invention a shear-resistant lubricating grease suitable for use in the lubrication of high speed ball and roller bearings at temperatures down to 100" F. comprises a liquid lubricating oil base consisting of a major proportion of an oil-soluble high-boiling dicarboxylic acid ester of lubricating characteristics having a viscosity within the range of about 6 to 10 centistokes, and preferably about 7 to 9 centistokes at 100 F., with a minor amount of a mineral lubricating oil having a viscosity within the range from about 14 to 30 centistokes at 100 F., thickened to a grease consistency with a lithium soap, the acid component of which comprises at least a major proportion of a hydroxy fatty acid. The composition is preferably slightly alkaline with about 0.05 to 1.0 per cent of free alkalinity calculated as lithium hydroxide. It also preferably contains a small but effective amount of an oxidation inhibitor such as is commonly employed to inhibit the oxidation of greases in the presence of metals including copper. Amine type oxidation inhibitors, such as for example diphenylamine, are particularly suitable. Various other lubricant additives such as extreme pressure agents may also be present.

The aliphatic diesters whichare employed as the major oil component in the above compositions are preferably branched chain diesters of adipic, azelaic or sebacic acids, obtained by reacting these acids with suitable branched chain or secondary alcohols, as for example di- 2-ethylbutyl azelate, di-Z-ethylhexyl adipate, di-l-ethylpropyl sebacate and so forth. Di-secondary amyl sebacate is a particularly suitable material of this character.

The mineral lubricating oil may be a naphthenic, paratfinic or mixed base oil obtained by any of the conventional refining procedures. It is suitably a lightly refined parafiin base distillate oil, preferably within the viscosity range of about l827 centistokes at 100 F. It may comprise about to 10 per cent, and preferably about 5 to 8 per cent, by weight of the grease composition.

The lithium soaps are suitably those described'in U. S. 2,450,222, obtained from soap-forming fatty materials consisting of more than 50 per cent by weight of hydroxy soap-forming fatty materials selected from the group consisting of hydroxy fatty acids and hydroxy fatty acid glycerides. The hydroxy fatty acids are those containing at least 12 carbon atoms in the molecule and one or more hydroxyl groups, as well as mixtures thereof. The soap-forming fatty materials preferably consist of a major proportion of hydrog nated castor oil and a minor proportion of a saturated soap-forming fatty acid such as stearic acid, a mixture of hydrogenated castor oil and stearic acid in about a 3:1 proportion by weight being particularly suitable for forming the lithium soaps for use in the grease compositions of our invention. The lithium soap may comprise about 12 to 20 per cent, and preferably about 14 to 18 per cent by weight of he gr as omp s t n Auy suitable grease making procedure may be employed in the manufacture of these greases. They are most advantageously prepared by saponifying in the presence of the mineral oil component, dehydrating and finally mixing in the ester component and any additives employed.

The following examples are given in order to further disclose the invention. Example 1 is illustrative of greases in which a relatively low viscosity aliphatic diester is employed as the sole oil component, Example 2 is illustrative of greases in which a light mineral lubricating oil such ashas been employed heretofore in greases of this type is employed in admixture with the lowviscosity diester, and Example 3 is illustrative of the greases of our invention. In each case the method of preparation employed was that which was found to be optimum for producing a grease of the desired char acteristics.

EXAMPLE 1 A steam heated kettle equipped with a stirring mechanism was charged with 16.0 pounds of lithium 12- hydroxy stearate and 2.7 pounds of di-secondary amyl sebacate. The latter was a synthetically obtained ma terial having a fiash point, COC, of 375 F., a fire point, COC, of 415 F. and kinematic viscosities at 100 F. and 210 F. of 7.44 and 2.30 centistokes, respectively. The mixture was heated for four hours at 300 F. with stirring and an additional 42.0 pounds of di-secondary amyl sebacate then added gradually while the temperature was slowly dropped to 210 F. When the temperature of the mass was about 215 F., 03 pound of a commercial oxidation inhibitor was added consisting of 5 per cent salicylalaminoguanidine oleate and 95 per cent diphenylamine. A small amount of Aniline Yellow dye was also added. The grease was finally. drawn at a temperature of 180 F. and pumped through three 60 mesh screens. The product was a light colored buttery grease having essentially the following calculated composition by weight.

Per cent Lithium 12-hydroxy stearate 26.2 Di-secondary amyl sebacate 73.3 Oxidation inhibitor 0.5

EXAMPLE 2 The kettle was charged with 10.8 pounds of 10.3 per cent lithium hydroxide solution, 5.0 pounds of water, 9.0 pounds of hydrogenated castor oil (titer 76.5 C.,

sap. No. 184, hydroxyl value 148) and 5.0 pounds of mineral oil. The mineral oil was a mildly refined distillate fraction from a mixed base crude having a flash point, PM, of 300 F., a pour point of 65 F., and a kinematic viscosity at F. of 7.20 centistokes. The kettle contents were heated at 180200 F. with stirring for 4 hours and 2.9 pounds of triple pressed stearic acid added. The temperature was maintained at 180200 F. for an additional 1 hour and the kettle then shut down for 11 hours. The mixture was reheated to 300-315 F. and maintained at this temperature with stirring for 4 hours to complete the dehydration, and an additional 9.75 pounds of the mineral oil then added while the temperature was allowed to drop. At approximately 300180 F. 44.25 pounds of di-secondary amyl sebacate, as described in Example 1, were added. When the temperature of the mass was about 215 F. 0.4 pound of the commercial oxidation inhibitor described in Example 1 was added. A small amount of Aniline Yellow dye was added also. The grease was finally drawn at a temperature of F. and pumped through three 60 mesh screens. The product was a light colored buttery grease having essentially the following calculated composition by weight:

Per cent Lithium soap (75% hydroxy stearic acid, 25%

stearic acid) 16.3 Glycerine 1.3 Mineral oil 20.4 Di-secondary amyl sebacate 61.3 Oxidation inhibitor 0.5 Excess LiOI-I 0.2

EXAMPLE 3 The kettle was charged with 10.8 pounds of 10.2 per cent lithium hydroxide solution, 5.0 pounds of water, 9.0 pounds of hydrogenated castor oil and 5.0 pounds of mineral oil. The hydrogenated castor oil was the same as that employed in Example 2. The mineral oil was a moderately refined paraffinic distillate oil having a flash point, COC, of 400 F., a fire point, COC, of 445 F., a pour point of 20 F. and a kinematic viscosity at 100 F. of 20.7 centistokes; The kettle contents were heated at l80200 F. with stirring for 4 hours and 2.9 pounds of triple pressed stearic acid added. The temperature was maintained at 180200 F. for an additional 1 hour and the kettle then shut down for 15 hours. The mixture was reheated to 300-320 and maintained at this temperature with stirring for 4 hours to complete the dehydration, and the temperature then allowed to drop. At approximately 320190 F. 57.5 pounds of di-secondary amyl sebacate, as described in Example 1, were added. When the temperature of the mass was about 200 F. 0.4 pound of the commercial oxidation inhibitor described in Example 1 was added. About 0.002 pound of Aniline Yellow dye was also added at about this temperature. The grease was finally drawn at a temperature of 180 F. and pumped through three 60 mesh screens. The product was a light colored buttery grease having essentially the following calculated composition by weight:

Per cent Lithium soap (75 hydroxy stearic acid, 25%

stearic acid) 15.6 Glycerine 1.2 Mineral oil 6.6 Di-secondary amyl sebacate 75.9 Oxidation inhibitor 0.5 Excess LiOH 0.2

The table below gives the results of tests carried out upon the greases of the above examples comparatively with the requirements of the proposed government specification for a low temperature ball and roller bearing grease.

Table i 1 Proposed Grease Example 1 Example 2 Example 3 specification Free Fatty Acid, Percent Free LiOH, Percent ASTM Penetration:

Unworked.

Wmked- 260-330. Dropping Point, F 3 3 325 mm Apparent Viscosity, poises, 20 sec- 15,000 max.

onds l, -100 F. Low Temp. Torque. sec./rev.:

5 max. Evaporation, Percent:

20 hours 22 1.5 max.

23 hours 7 Oil Bleeding, Percent Loss 1.7; 2.3 2.8; 2.1.-. 2.0; 1.8 5 Low Temp. Torque on Residue at -100 F., sec/rev. 1.6; 1 1; 3.0.0.... 1; 1 5 max. N-H 100hr. Oxidation, p. s. 1. Drop 1; 2 5 max. oppe o o 25 Passes Passes Passes Must pass. MIL-G-3278: v

pp Brown sta1n Unchanged Sl1ghtgray Grease Reddish brown, do Unchanged Pressure Drop 0 Rating pass Water Resistance, Percent Los 20 max Working Stability, Penetration after 100,000 strokes 257 375 max Gear Wear Test:

5111-110 0.37 max. 10 A 3 5 n18 The copper corrosion test of military specification MlLG-32'l8 of the foregoing table is a rigorous test for determining the corrosiveness of a grease to copper in long time service. The test is run by placing a copper strip in a Norma-Hoffman bomb so as to be partially immersed in a sample of the grease under test, and then maintaining the bomb under oxygen pressure (110 pounds per square inch initial pressure) at 210 F. for 20 hours. During that period, a pressure drop of not more than 0.5 pound per square inch due to oxygen ab sorption must occur. At the completion of the 20-hour period, both the sample of grease and copper strip are inspected. In addition to the requirement for pressure drop during the test, there must be no more than a very faint stain on the copper strip and no more than a slight stain on the grease in order to be rated as passing.

As shown by the table, the grease of our invention very satisfactorily met all of the requirements of theproposed government specification for a low temperature instrument grease and in addition it met the rigorous MIL-G-3278 copper corrosion test. In comparison with the grease wherein the diester was employed as the sole oil component, it showed less tendency to change or harden in the working stability test, satisfactorily passed the MIL-G3278 copper corrosion test while the straight diester grease failed, and was at least equivalent in all other lubricating properties. In addition it required only 15.6 per cent of lithium soap, as compared with 26.2 per cent of lithium soap for the grease prepared without the mineral oil component. The grease which was prepared employing as the oil component a mixture of the diester with a larger amount of a light mineral oil of the type employed heretofore in low temperature greases of this type had both a too high evaporation loss and a too high low temperature torque to meet the requirements of the proposed specification.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim: 1. A lubricating grease composition consisting essentially of an oleaginous liquid base as the predominant 7 fatty material selected from the group consisting of hydroxy stearic acid and hydroxy stearic acid glyceride, and a minor proportion of a saturated soap-forming nonhydroxy fatty acid, said oleaginous liquid base consisting of an oil-soluble high-boiling aliphatic dicarboxylic acid diester having a viscosity within the range from about 6 to 10 centistokes at 100 F., selected from the group consisting of branched chain diesters of adipic, azelaic and sebacic acids with C5-C3 alcohols, and about 5 to 8 per cent by weight based on the weight of the composition of a mineral lubricating oil having a viscosity within the range from about 14 to 30 centistokes at 100 F., said grease having an ASTM worked penetration in the range 260-330 and a low temperature torque test below 5 seconds per revolution at 100 F.

2. A lubricating grease composition according to claim 1, wherein said aliphatic dicarboxylic acid diester is disecondary amyl sebacate.

3. A lubricating grease composition according to claim 1, wherein said composition contains about 0.05 to 1.0 per cent of free alkalinity calculated as lithium hydroxide.

4. A lubricating grease composition according to claim 1, wherein said soap-forming fatty material consists of a major proportion by weight of hydrogenated castor oil and a minorproportion of stearic acid.

5. A lllbllCZltlIlg grease composition consisting essentlally of the following ingredients in per cent by weight:

Lithium soap of an approximately 3 :1 mixture 6. A lubricating grease composition according to claim 5, wherein said mineral lubricating oil is a parafiin base distillate oil.

References Cited in the file of this patent UNITED STATES PATENTS 0 2,450,221 Ashburn et al 2,450,222 Ashburn et a1 is 2,491,028 Beerbower et a1. Dec. 13 1949 2,491,054 Morway Dec. 13 1949 2,576,032 Morway Nov. 20 1951 5 2,589,973 Smith et a1 Mar. 18: 1952 

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF AN OLEAGINOUS LIQUID BASE AS THE PREDOMINANT CONSTITUENT THICKENED TO A GREASE CONSISTENCY BY ABOUT 12 TO 20 PER CENT BY WEIGHT BASED ON THE WEIGHT OF THE COMPOSITION OF A LITHIUM SOAP OF A SOAP-FORMING FATTY MATERIAL, SAID SOAP-FORMING FATTY MATERIAL CONSISTING OF A MAJOR PROPORTION BY WEIGHT OF A HYDROXY SOAP-FORMING FATTY MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROXY STEARIC ACID AND HYDROXY STEARIC ACID GLYCERIDE, AND A MINOR PROPORTION OF A SATURATED SOAP-FORMING NONHYDROXY FATTY ACID, SAID OLEAGINOUS LIQUID BASE CONSISTING OF AN OIL-SOLUBLE HIGH-BOILING ALIPHATIC DICARBOXYLIC ACID DIESTER HAVING A VISCOSITY WITHIN THE RANGE FROM ABOUT 6 TO 10 CENTISTOKES AT 100* F., SELECTED FROM THE GROUP CONSISTING OF BRANCHED CHAIN DIESTERS OF ADIPIC, AZELAIC AND SEBACIC ACIDS WITH C5-C8 ALCOHOLS, AND ABOUT 5 TO 8 PER CENT BY WEIGHT BASED ON THE WEIGHT OF THE COMPOSITION OF A MINERAL LUBRICATING OIL HAVING A VISCOSITY WITHIN THE RANGE FROM ABOUT 14 TO 30 CENTISTOKES AT 100* F., SAID GREASE HAVING AN ASTM WORKED PENETRATION IN THE RANGE 260-330 AND A LOW TEMPERATURE TORQUE TEST BELOW 5 SECONDS PER REVOLUTION AT -100* F. 